April 1, 2012
By Catherine Lemieux, P.Eng., LEED AP
When looking at its skyline, it is no wonder why Vancouver is known as the “City of Glass.” Glass high-rise buildings, each one taller than the next, have been the architectural vision developed over many years (Figure 1). In fact, the relationship between West Coast architecture and glazing systems is symbiotic; their evolution would not have been possible without one another. This article discusses the last 20 years of glazing progression in the Lower Mainland market. (The author would like to thank Mark Lawton and Sophie Mercier for their insight and experience relating to the evolution of glazing across Canada).
Back in the 1980s, punch windows were the traditional glazing choice for buildings across Canada. The units were rebate-mounted into the rough openings, meaning fasteners were driven through the sides of the frame into the wall structure. Effort was required to ensure the windows were level and plumb.
The Vancouver area was facing a growth in the construction sector, leading to a bigger, but less experienced, workforce. This was driving the need to develop an easier means for installing the windows within the rough openings. It was then the nailing flange started to be incorporated into window frame manufacturing. The idea was the installer would simply place the frame into the rough opening until the nailing flange stopped it from going in further, and then fasteners were driven through the face of the flange into the wall (Figure 2). This practice became somewhat unique to Canada’s West Coast. In fact, the standards of the time––such as the 1990 edition of Canadian Standards Association (CSA) A440-M90, Windows––did not even recognize flange-mounted windows.
With the evolution of aluminum glazing systems, the nailing flange has gradually disappeared. Many of today’s vinyl windows, however, can still be found with flanges––some are still monolithic to the vinyl extrusion while others add the flanges in a chase afterward. The latter style cannot rely on the flange as being a means for structural attachment––it is purely an installation guide.
The leaky condo crisis
With residential construction still on the rise in the 1990s, the design trend favoured larger vision areas in the walls. The typical aluminum window frame consisted of the same extrusion used at the head, sill, and jambs, joined together at mitre corners. In terms of water shedding, the extrusions themselves were not sloped to the outside. Limited means for drainage was provided within the frame.
At the inside face of the sill, an interior track was incorporated into the frame to collect condensation, which could be drained back to the outside through weep holes. During wind-driven rain, the differential pressure across the system would often result in the height of the water within the track to be more than a shallow track could handle, leading to water spilling over to the inside. The insulated glass (IG) units were glazed from the outside with glazing stops having no provision for weatherseals, thus inviting more water into the system than desired. The combination of these features meant this window style was at high risk of suffering from water leakage.
While the window construction was an issue in itself, another critical factor was there was no real effort placed on waterproofing of the rough openings. Leakage through the window frame often resulted in water getting into the wall cavity below and, consequently, deterioration of the finishes and structural elements.
From a thermal performance perspective, there was a false sense that, given Vancouver’s milder climate, installing non-thermally broken windows was an acceptable practice. The 1990 edition of CSA A440-M90, Section 8.1 states:
except for storm windows, all metal windows covered by this Standard shall incorporate a thermal break to prevent through-metal conductivity.
While other governing bodies across Canada were mandating windows follow this standard, Section 126.96.36.199 of the 1992 British Columbia Building Code (BCBC) clearly stated “windows need not incorporate a thermal break.” Since installing windows with poor thermal performance was allowed by this clause, condensation became a common issue in many buildings of this era.
Aside from condensation, the earlier thermal breaks were prone to shrinkage over time, such that they opened up at the corners of the frames. This additional source of water infiltration, combined with inadequate waterproofing of the rough openings, compounded the problem. In fact, non-thermally broken frames performed better from a watertightness perspective at the mitre corners compared to the first versions of the thermally broken windows (Figure 3).
Punch windows became larger and slimmer in profile until they were installed from slab to slab. The framing elements were quite slim compared to today’s systems. It has been debated by some that the aluminum systems of the early 1990s may have been used in configurations beyond their structural capacities. The windows were designed with limited engineering and, as such, the systems were bridging increasingly larger spans and were becoming much more flexible. In turn, the windows’ primary seals were being challenged as the flexible frames moved beyond today’s tolerances with wind loading, building settlement, and thermal expansion and contraction.
Failures of the seals and the misalignment of mitre joints within the framing––especially when looking at aluminum frames with no second line of defence against moisture (particularly subsill flashings) or in adequate water management capabilities––were a characteristic source of water penetration into the buildings.
All these factors contributed in part to the West Coast’s ‘leaky condo crisis,’ and the severity of the repercussions can still be felt today as building envelope rehabilitations of structures from that era are still a reality. However, the crisis did lead to significant improvements to glazing systems. Local window manufacturing companies became more prominent in the market and started including features such as sills sloped to drain and stops with weatherseals. Joinery at the mitre corners remained a weak point in the aluminum windows, which meant vinyl windows with welded corners became a more popular choice for low-rise residential buildings. Engineers and installers developed the technique of installing subsill flashings at the rough openings to help manage moisture, even if the mitre corners leaked. The 1998 BCBC also evolved and started mandating thermal breaks within aluminum frames to minimize the risk of condensation.
Window walls came to the West Coast from Eastern Canada, and consisted of thermally broken aluminum frames that included a slab bypass section. This was essentially the same frame configuration as the vision area, but with the framing inboard of the thermal break simply cut off so it fit in front of the slab edge. This technology became very popular for residential towers, and local manufacturers started copying the idea.
Earlier versions of the system did see their fair share of failures, but over time they were refined. This is especially true when considering the move to moisture management design started as a face-sealed style, meaning the window’s outer surface was intended as the primary moisture barrier and did not include any provision to deal with moisture getting past the outer surface. The face-sealed design moved toward a hybrid approach that included a poor means of drainage, to finally the rainscreen approach the industry now knows. The rainscreen design incorporated redundancy by having two separate lines of defence against moisture and efficient drainage.
The technique of flashing at each floor slab was developed in the Vancouver area and became the norm across the country. The benefit of this practice, aside from moisture management, was each floor could be sealed off from the elements as the frames are erected (Figure 4). This technique was a significant advantage to the contractor as the installation of interior finishes could start sooner in the construction process.
Architecturally, the window wall gave high-rises the all-glass look of a curtain wall at a more competitive cost. The depth of the frames could be increased from 100 to 150 mm (4 to 6 in.) to achieve longer spans. Different planes of the glazing within the frame were another architectural option.
Curtain wall systems
Stick-built curtain wall systems had been around for a while within the Vancouver area and were mainly used at podium entrances and inset into rough openings in low-rise buildings. Unitized curtain wall systems are a more recent addition to the West Coast. Aside from its more conventional use on commercial towers, the unitized curtain wall is also becoming common in residential towers because of the growing complexity of the local architecture. Curtain wall design needed to accommodate condominium features like balconies, roof decks, and sliding glass doors. (One recent example of curtain wall used in a residential tower is illustrated in the article’s first photo, the Jameson House, designed by Norman Foster and Walter Francl Architects. The curtain wall system was designed by a local firm and manufactured by an offshore firm).
There are numerous B.C. firms that have developed fairly sophisticated unitized systems over the past years, but with so many other companies globally, the competition is fierce. A few local firms have become more renowned because of their ability to customize their systems––both two-sided and four-sided structural silicone glazing, depending on the project at hand.
With recent shifts in the global economy, new offshore curtain wall suppliers are competing for Vancouver area business––from South Korea and China, for example. While the main attraction is the lower cost of offshore systems while usually maintaining high-quality standards, their use in Canada comes with some considerations. For example, frames are built according to drawings rather than site measurements, such that they sometimes need to be modified onsite to suit construction tolerances. Shipping schedules can also have an impact on the project. Replacement of certain components over the system’s service life could be difficult and costly if local resources cannot provide exact matches in glass shape or coatings.
The evolution of the various glazing systems would not be the same without the emphasis on performance testing. As a direct result of the leaky condo crisis, the 1998 Homeowner Protection Act requires a third-party warranty for all new home construction and building envelope rehabilitation projects, with some exceptions. Third-party warranty providers in British Columbia have in turn required windows meet the minimum level of water penetration resistance when tested to a differential pressure of 300 Pa (0.04 psi)––formerly a B3 rating according to CSA A440-00.
Site testing to ASTM E 1105, Standard Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls, by Uniform or Cyclic Static Air Pressure Difference, is now accepted practice in Vancouver, unlike the rest of Canada (Figure 5). (Field-testing has been mandated by the third-party warranty providers on multi-unit residential buildings in the Lower Mainland, and has since been adopted by the commercial and institutional projects as well, making it more common than in the rest of Canada). As a result, window manufacturing needed to be better and more consistent, and contractors had to adjust their installation methods as they learned from failed tests. Glazing systems have been refined to a point where the performance level is generally higher in the Vancouver area than many other areas. Additionally, the requirement for laboratory mockup testing has increased, especially with customized systems.
Achieving energy efficiency
The various components within the glazing systems have also evolved. In aluminum frames, the polyurethane pour and debridge thermal breaks have been more or less replaced by polyamide strip thermal breaks. Originally considered ‘high-end,’ the strips are now ubiquitous.
Significant advances have also been made in insulated glass units. Stainless steel and aluminum spacers now incorporate polyurethane thermal barriers. Some spacers eliminated the metal component and consist solely of foam. Triple-glazed IG units are also an option being incorporated into glazing systems. Another important element is the glass coating. Low-emissivity (low-e) glass coatings have been in existence since the 1980s, but were often value-engineered out because of questionable energy modelling practices occurring specifically in British Columbia. With more stringent building code requirements, standards, and green rating programs, the quality of the IG units has improved.
Striving to meet new energy requirements has opened up the market to exploring entirely different materials. As of 2011, under B.C.’s Energy Efficiency Act, aluminum windows needed to achieve a maximum U-value of 2.0 W/(m²K) in low-rise buildings; for high-rises, the maximum U-value is 2.57 W/(m²K). This target has been difficult to meet for many manufacturers. With aluminum windows not meeting energy requirements, and vinyl windows having limited structural capacities, fibreglass windows have become a new alternative. They are more similar in appearance to typical aluminum profiles, yet much stronger than vinyl. Their thermal resistance also competes with that of vinyl.
Fibreglass frames are a fairly recent addition to the readily available glazing systems in Canada. Their thermal properties make them desirable, but they still have hurdles to overcome––the biggest being combustibility. In the 2006 BCBC, Sections 188.8.131.52.5. (b) and (c), “Combustible Glazing” and “Skylights,” respectively, combustible windows can be installed in noncombustible buildings provided:
windows in exterior walls in contiguous storeys are separated by not less than 1 m of noncombustible construction [and] the aggregate area of openings in an exterior wall face of a fire compartment is not more than 40 per cent of the area of the wall face.
This may not seem like a challenge for most of Canada, but the clause is at odds with West Coast architecture.
Glazing systems have changed significantly on the West Coast over the past 20 years, by borrowing from other practices across the country and the world, and by developing details and techniques specifically in the Vancouver area. Lessons learned from failures made vast improvements and have propelled the industry to where it is today.
The focus to construct better buildings from an energy efficiency standpoint directly affects the development of glazing components and entire systems. Time will tell if modern systems, like fibreglass, fulfil their promise. Ultimately, glazing is a dominant feature of building architecture, and the evolution of one cannot be without the other. Perhaps the City of Glass will need a new moniker in another 20 years.
Catherine Lemieux, P.Eng., LEED AP, is a building science consultant at Morrison Hershfield’s Vancouver office. She has been with the company for six years. Lemieux has participated in projects ranging from the diagnosis of building envelope failures and the rehabilitation work on existing buildings, to design and field review for new construction projects spanning the residential, commercial, and institutional sectors. She is a member of the Association of Professional Engineers and Geoscientists of British Columbia (APEGBC) and the British Columbia Building Envelope Council (BCBEC). Lemieux can be contacted via e-mail at firstname.lastname@example.org.
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